In a liquid crystal display device, a TFT substrate includes pixel electrodes, thin film transistors (TFTs), and the like, arranged in a matrix form. A counter substrate includes color filters, and the like, arranged at positions corresponding to the pixel electrodes of the TFT substrate. Liquid crystal is interposed between the TFT substrate and the counter substrate. In this configuration, the liquid crystal display device forms an image by controlling the transmittance of light of the liquid crystal molecules for each pixel.
The liquid crystal display device is flat and light weight, and is used in a wide range of applications in various fields. Small liquid crystal display devices are widely used in electronic devices such as mobile phone and DSC (Digital Still Camera). In the electronic devices such as mobile phone and DSC, there is a demand for reducing the thickness of the whole device in addition to reducing the weight. This leads to a strong demand for using a liquid crystal display device with the entire thickness reduced.
It is not efficient if small liquid crystal display devices are manufactured individually. Thus, the following method is used in order to increase the manufacturing efficiency. First, a mother TFT substrate in which a large number of TFT substrates are formed is manufactured. Also, a mother counter substrate in which a large number of counter substrates are formed is manufactured. Then, the mother TFT substrate and the mother counter substrate are bonded together to form a mother panel. Then, individual liquid crystal cells are cut off from the mother panel.
Meanwhile, in order to meet the demand for reducing the thickness of the liquid crystal display panel, it is necessary to reduce the thicknesses of the TFT substrate and the counter substrate that constitute the liquid crystal display panel. In recent years, the thickness of the TFT substrate or the counter substrate has been reduced to about 0.2 mm, or in some cases to about 0.15 mm. However, such a thin glass plate is not available as a standardized product. In addition, such a thin glass substrate has a low strength, and is difficult to be processed in the manufacturing process.
For this reason, a standardized glass substrate of 0.5 mm or 0.4 mm is used in the stage of forming a mother TFT substrate or mother counter substrate. Then, the mother TFT substrate and the mother counter substrate are bonded together to form a mother panel. Then, the outside of the mother panel is polished to reduce the thickness. The polishing is performed in combination of mechanical and chemical polishing methods. The mother TFT substrate or mother counter substrate is polished to a thickness of about 0.15 mm to 0.25 mm.
The chemical polishing tends to first polish the end portion of the glass substrate. Thus, after the chemical polishing, the thickness of the end portion of the mother panel is small. In particular, the mechanical strength is reduced in this portion, which is likely to cause a crack or cleft. Scribing is performed based on the outline of the mother panel in separating the individual liquid crystal cells from the mother panel. When the end portion of the mother panel is weakened and is cracked or damaged, the accuracy of the scribing is reduced.
JP-A No. 317983/2004 describes a technology that forms a coating portion of resin in a peripheral end portion of the mother panel, preventing the occurrence of such a thin end portion of the mother panel when the thickness of the mother panel is reduced by the chemical polishing. In this way, the technology of JP-A No. 317983/2004 is designed to ensure the thickness and strength of the end portion of the mother panel to increase the accuracy of the scribing.